Plant lectins, also known as “agglutinins”, are heterogeneous group of carbohydrate binding proteins, which are able to bind simple sugars and/or complex carbohydrates reversibly (Van Damme et al. 1998; CRC Crit Rev Plant Sci 17:575-692). They show a marked heterogeneity with respect to their molecular structures, sugar binding specificity and temporal and spatial regulation. Mannose binding lectins are widely found in higher plants and play a significant role in defense due to their ability to recognize high-Mannose-type glycans of microbial pathogens and plant predators (Van Damme et al. 1998, 1998, CRC Grit Rev Plant Sci 17:575-692; Van Damme et al. 2004 Trends Plant Sci 9:484-9). Mannose binding lectin from garlic leaf [Allium sativum leaf agglutinin (ASAL)] is a 25 kDa homodimeric protein, structurally and evolutionarily related to Galanthus nivalis agglutinin (GNA) (Smeets et al. 1997a, Plant Mol Biol 35: 531-535; Van Damme et al. 1992, Eur J Biochem 206:413-420). Some of the biological properties of ASAL are—(1) it readily agglutinates rabbit erythrocytes but does not affect human erythrocytes (Bandhopadhyay et. al. 2001, Plant Sci. 161:1025-1033; Smeets et al. 1997a, Plant Mol Biol 35: 531-535), (2) it has inhibitory effect against retrovirus (HIV1 and HIV2) induced cytopathicity in MT-4 cells (Smeets et. al. 1997b, Plant Mol Biol 33:223-234) and (3) it is toxic (growth inhibitory) against a spectrum of insects of order Homoptera, Lepidoptera and Coleoptera. Some important pests inhibited by ASAL are aphids [mustard aphid, peach potato aphid, tobacco aphid (Bandhopadhyay et al. 2001, Plant Mol Biol 33:223-234 Hossain et al. 2006, Crop Sci 46:2022-2032; Smeets et al. 1997a, Plant Mol Biol 35: 531-535), red cotton bug (Bandhopadhyay et al. 2001, Plant. Mol. Biol. 33:223-234), brown plant hopper, green leaf hopper (Saha et al. 2006, Plant Mol. Biol. 62:735-52) and cotton leaf worm (Sadeghi et al. 2008, Transgenic Res. 17:9-18). Although exact mechanism of insecticidal action of lectins is still not well understood, three different modes of action have been proposed—(1) binding of the lectins to the peritrophic matrix of the midgut, inhibiting nutrient absorption (Harper et al 1998, Tissue Cell 30: 166-176), (2) binding to glycoproteins on epithelial cells of the midgut and disrupting tissue integrity (Powell et al. 1998, J Insect Physiol. 44: 529-539; Sauvion et al. 2004, J Insect Physiol. 50: 1137-1150) and (3) binding to carbohydrate moieties of the sensory receptors of insect mouth parts, disrupting membrane integrity and interfering in the food detection ability of insects (Murdock et al. 2002, J Agric Food Chem. 50: 6605-6611). All these mechanisms result in decreased ability of insect to ingest food or absorb nutrients, leading to delayed development and premature death.
U.S. Pat. No. 5,545,820 (Gatehouse, et al., 1996) discloses the use of lectins having specific mannose-binding ability, derived from family Amaryllidaceae or Alliaceae for the control of insect pests. WO/1992/002139 relates to the use of lectins having specific mannose-binding ability, derived from family Amaryllidaceae or Alliaceae for the control of insect pests and the development of transgenic plants expressing such lectins. U.S. Pat. No. 5,407,454 relates to selected plant lectins having larvicidal activity against a number of common insect pests of agricultural crops. Insect resistance in the transgenic plants is due to insertion of larvicidal lectin gene in all the cells of the plants.
U.S. Pat. No. 6,127,532 (Raikhel) refers to transgenic plants containing cDNA encoding Gramineae lectin. Such transgenic plants expressed barley lectin and stored in in the leaves. The transgenic plants, particularly the leaves exhibit insecticidal and fungicidal′ properties.
Allium fistulosum 
Allium fistulosum L. (Welsh onion, Japanese bunching onion) is a perennial onion. Other names that may apply to this plant include green onion, spring onion, escallion, and salad onion. These names are ambiguous, as they may also be used to refer to any young green onion stalk, whether grown from Welsh onions, common bulb onions, or other similar members of the genus Allium. The species is very similar in taste and odor to the related bulb onion, Allium cepa, and hybrids between the two (tree onions). The Welsh onion, however, does not develop bulbs, and possesses hollow leaves (“fistulosum” means “hollow”) and scapes. Large varieties of the Welsh onion resemble the leek, such as the Japanese ‘negi’, whilst smaller varieties resemble chives. Many Welsh onions can be multiplied by forming perennial evergreen clumps. Next to culinary use, it is also grown as an ornamental plant. Historically, the Welsh onion was known as the cibol.
The name “Welsh onion” has become a misnomer in modern English, as Allium fistulosum is not indigenous to Wales. “Welsh” preserves the original meaning of the Old English word “welisc”, or Old German “welsche”, meaning “foreign” (compare wal- in “walnut”, of the same etymological origin). The species originated in Asia, possibly Siberia or China.
Culinary Use
In the West, the Welsh onion is primarily used as a scallion or salad onion, but is widely used in other parts of the world, particularly East Asia.    Russia: Welsh onion is used in Russia in the spring for adding green leaves to salads.    Asia: The Welsh onion is an ingredient in Asian cuisine, especially in East and Southeast Asia. It is particularly important in China, Japan, and Korea, hence the other English name for this plant, ‘Japanese bunching onion’. Bulb onions were introduced to East Asia in the 19th century, but A. fistulosum remains more popular and widespread. In Japan, it is used in miso soup, negimaki (beef and scallion rolls), among others, and it is widely sliced up and used as a garnish on teriyaki or takoyaki.    Jamaica: Known as escallion, the Welsh onion is an ingredient in Jamaican cuisine, in combination with thyme, scotch bonnet pepper, garlic and allspice (called pimenta). Recipes with escallion sometimes suggest leek as a substitute in salads. Jamaican dried spice mixtures using escallion are available commercially. The Jamaican name is probably a variant of scallion, the term used loosely for the spring onion and various other plants in the genus Allium. Lacking in the Prior Art
Allium lectin disclosed in present invention shows high insecticidal activity and therefore novel. Homology of the nucleotide sequence with available nucleotide sequences in database shows more than 90% homology.